1. Field of the Invention
The present invention relates to a process for producing with high productivity a steel wire rod with minimal decarburized layer on the surface and having excellent cold forgeability, which process comprises controlling the rolling process of the hot rolled wire rod so as to give a predetermined thickness of scale and a rapidly cooled structure to the wire rod, and spheroidizing annealing this wire rod having the rapidly cooled structure and the predetermined thickness of scale thereon in an inert gas such as N.sub.2 gas.
2. Description of Prior Art
Generally, in the cold forging of medium carbon steels or low-alloy steels which are relatively hard and have a low forgeability, the steels are usually subjected to spheroidizing annealing in order to spheroidize the carbides therein and thus to improve their cold forgeability.
In ordinary hot rolled steel wire rods, the carbides constitute a coarse lamellar pearlite structure and, in order to spheroidize these carbides, the steel is usually held at a temperature immediately above the A.sub.1 transformation point for several hours, slowly cooled, and then held at a temperature immediately below the A.sub.1 transformation point for several hours. The treatment thus requires considerable time.
During this long period, oxidizing gases in spheroidizing annealing atmosphere promote the decarburization of the steel surface. For prevention of such surface decarburization, the annealing is done in a reducing gas atmosphere. However, if scale exists on the steel surface, this scale reacts with the reducing gas to locally generate an oxidizing gas which promotes the surface decarburization. Therefore, it has been necessary to acid-pickle the hot rolled wire rods in order to remove the scale prior to the spheroidizing annealing.